The drilling of wells, such as those for oil and gas often use a top drive to turn the drillstring. The quill of the top drive typically threads into the box end of the top joint of pipe used for drilling and in turn drives the pipe. The problem encountered is that there is potential for damage to the threads of both the drill pipe and the top drive quill. Galling of the threads is undesirable, since they have to be machined to correct the damage, which is time consuming and costly, especially given the typically remote locations that wells are drilled in. It is especially desirable to avoid damaging the threads on the top drive, since they are much more difficult and expensive to repair than drill pipe.
With the development of drilling with casing, that is using a casing string as the drill pipe, the issue of thread protection has become much more important. This is because the thread form used in casing connections is more fragile than the connections used in drill pipe, and the casing connections have to remain fluid and pressure tight once the drilling process has been completed. Other considerations are that casing typically has a thinner sidewall and is less robust than drill pipe. This is especially true in the thread area, where the casing has threads on both ends, with a corresponding reduction in section area.
While some clamps are available for gripping casing, these clamps grip the casing on the inside using expandable jaws. These clamps are therefore not suitable for use in manipulating casing during a casing drilling operation. The expandable jaws create a severe restriction on the casing's inner diameter which restricts mud flow downhole, for example, to a downhole motor which may restrict the amount of power the motor is capable of producing. In addition, the jaws are not fail safe, since a biasing agent must be continuously applied to maintain gripping force. Prior casing clamps had no means for passing fluids to the casing bore and had no means for manipulating the casing simultaneously in vertical and rotational directions.
Other prior methods of handling casing involved using the kelly or top drive to turn the casing, with the attendant risk of damage to the threaded connections. A safer and more efficient system of driving a casing string is needed.